In accordance with ASTM definitions, masonry cement is defined as a hydraulic cement for use in mortars for masonry construction, containing one or more of the following materials: portland cement, portland blast-furnace slag cement, portland-pozzolan cement, natural cement, slag cement, or hydraulic lime; and in addition usually containing one or more materials such as hydrated lime, limestone, chalk, calcareous shell, talc, slag, or clay, as prepared for this purpose. The present physical requirements for mortars to meet ASTM specifications are as follows:
______________________________________ Fineness, residue on a 45-.mu.m (No. 325) sieve, max, % 24 Autoclave expansion, max, % 1.0 Time of setting, Gillmore method: Initial set, min, h 2 Final set, max, h 24 Compressive strength (average of 3 cubes): The compressive strength of mortar cubes, composed of 1 parts cement and 3 parts blended sand (half graded standard sand, and half standard 20-30 sand) by by volume, prepared and tested in accor- dance with this specification shall by equal to or higher than the values specified for the ages indicated below: 7 days, psi 500 (MPa) (3.45) 28 days, psi 900 (MPa) (6.21) Air content of mortar, prepared and tested in accordance with requirements of this specification: Min. volume % 12 Max, volume % 22 Water retention, flow after suction, min, % or original flow 70 ______________________________________
To achieve these test results, mortars are prepared from the masonry cement of the present invention by proportioning the masonry cement to contain the weight of cement, in grams, equal to six times the printed bag weight in pounds (13.228 times the printed bag weight in kilograms) and 1440 g of sand as outlined in ASTM C-91. The sand shall consist of 720 g of graded standard sand and 720 g of 20-30 standard sand also as outlined in ASTM C-91. The quantity of water, measured in milliliters shall be such as to produce a flow of 110.+-.5 as determined by the ASTM flow table.
A typical prior art masonry cement contains approximately 50% portland cement, 42% high grade limestone and approximately 8% of other components, including an air entraining agent. Typically, masonry cements are manufactured by using a steel ball grinder to grind the limestone with the other components for admixture with the portland cement. These prior art masonry cements require a relatively high percentage i.e. 42% of limestone as a plasticizer to meet ASTM specifications for masonry cements. ASTM specifications for air content in a masonry cement are in the range of 12-22% by volume to provide void spaces in the masonry cement for durability since masonry cements require voids for expansion of freezing moisture.
The use of a substantial quantity of limestone as a plasticizer in prior art masonry cements creates two significant problems. First, the substantial quantities of limestone necessary to provide sufficient plasticity to the masonry cement reduces the compressive strength of the cement. Second, the limestone must be crushed in a grinder together with other components, such as a polyglycol, fatty acids, and a sucrose solution, to provide a slurry for admixture with the portland cement. The grinder must be carefully cleaned after each batch so that the masonry cement can be manufactured as a consistent, precise composition. Further, if the masonry cement composition is to be changed between batches, the grinder must be completely cleaned after each batch to make sure that the masonry cement being manufactured meets the ASTM specification for the particular type of masonry cement since it may be prohibitive for a particular type of masonry cement to include a component of the masonry cement previously included in the last limestone grinding batch.